1. Field of the Invention
The present invention relates to a battery pack that can change the maximum charging voltage of a rechargeable battery to select a high capacity mode in that the fully-charged capacity of a rechargeable battery can be higher or a long life mode in that the cycle life of the rechargeable battery can be longer, and in particular to a battery pack that can easily acquire a relative remaining capacity of a rechargeable battery depending on a selected operation mode.
2. Description of the Related Art
Electronic devices such as note personal computer (PC) often include a battery packs that serves as a power supply portion, and includes a rechargeable battery and a controlling/calculating portion for controlling charging/discharging operation of the rechargeable battery. A rechargeable battery in this type of battery pack is charged from an external power supply (commercial power supply) via a power supply portion of an electronic device, for example, and supplies electronic power to the electronic device instead of the external power source when the electronic device is disconnected from the external power source.
An example of the rechargeable batteries can be provided by lithium ion battery. The characteristics of lithium ion battery, in particular, the charged capacity and the cycle life of lithium ion battery vary in accordance with charging voltage, as shown in FIG. 6. Specifically, when a rechargeable battery (lithium ion battery) is charged to a higher voltage as the maximum charging voltage, the charged capacity of the rechargeable battery can be higher but the cycle life of the rechargeable battery will be shorter as shown by a property line A in FIG. 6. Conversely, when a rechargeable battery (lithium ion battery) is charged to a lower voltage as the maximum charging voltage, although the charged capacity of the rechargeable battery will be lower, the cycle life of the rechargeable battery can be longer as shown by a property line B in FIG. 6.
From the characteristics of rechargeable battery, it has been conceived that voltages as the maximum charging voltage are selected in charging operation of the rechargeable battery so that the battery pack are selectively used in a high capacity (RT) mode and a long life (LS) mode (see Japanese Patent Laid-Open Publication No. 2002-78222, for example).
Specifically, the rechargeable battery (lithium ion battery) is charged to the maximum charging voltage of 4.2 V/cell in the high capacity mode, and is charged to the maximum charging voltage of 4.1 V/cell.